The present invention is directed to a flow modulating device used to control and monitor airflow. In particular, the device is intended to modulate and monitor the amount of fresh air being provided to the air conditioning system of a building. In an alternative embodiment, the device also mixes the fresh air with return air. Circuitry to improve the resolution of airflow measurement is also described.
Indoor air quality (IAQ) affects everyone involved with building design, construction, operation, use and maintenance. Sick buildings can result in sick occupants; sick occupants are less productive, don't renew their leases, and tend to sue everyone involved.
Consequently, building system designers must comply with the requirements of ASHRAE Standard 62-89 "Ventilation for Acceptable Indoor Air Quality". In broad terms, ASHRAE 62-89 specifies requirements intended to control microbial growth and to provide adequate ventilation for contaminant dilution. Included are two methods of providing adequate ventilation: the ventilation rate procedure and the indoor air quality (IAQ) procedure. The ventilation rate procedure specifies minimum outdoor airflow rates for adequate dilution, while the indoor air quality procedure specifies contaminant levels and subjective evaluation for acceptable indoor air quality. Most designers choose the ventilation rate procedure since it is prescriptive and seems less risky than the IAQ procedure. Designers tend to avoid the IAQ procedure because it seems open ended and subject to multiple interpretations.
The ventilation rate procedure provides a prescriptive path to compliance. It defines acceptable indoor air quality in terms of minimum ventilation airflow for contaminant dilution. A table lists ventilation airflow requirements for spaces and a simple equation determines system level outdoor airflow requirements for multiple space systems. Many designers prefer the ventilation rate procedure since it presents an objective ventilation design approach.
Devices for controlling the intake of fresh air are known. For example, U.S. Pat. No. 4,200,117 to Anderson et al. shows a device including a pair of closure members pivoted relative to a transverse axis and biased to the closed position by a spring. U.S. Pat. No. 5,324,229 to Weisbecker shows a two section damper including a fresh air inlet and a mixing section to prevent stratification. U.S. Pat. No. 5,276,630 to Baldwin et al. also discloses an outside air connection controlled by a damper. The Baldwin et al. patent and the Weisbecker patent are assigned to the assignee of the present invention and are hereby incorporated by reference.